In the past, as a method to uniformly correct the unevenness of the skin, such as prominence of pores and fine wrinkles, the blurring effect due to diffuse reflection with spherical powder has been used.
Especially lately, in order to achieve such an effect, spherical resin powders with a low refractive index, such as PMMA and nylon, and spherical inorganic powders with a refractive index of approximately 1.5-2.0, such as barium sulfate and alumina, have been used. In addition, composite powders with increased diffuse reflection prepared by uniformly attaching spherical resin powder on the surface of flaky powder such as talc, mica, alumina, or barium sulfate, are being developed. Composite powders with the increased blurring effect, which is achieved with the improved light diffusion due to the increased refractive index by forming a titanium oxide layer and a silica layer on the surface of spherical silica particles, have also been developed.
On the other hand, titanium oxide pigment with a refractive index of 2.69, which has good hiding power and coloring ability, has been used to correct imperfections in skin color, such as dullness, blotches, freckles, redness, and dark rings around the eyes.
The correction based on the spectral characteristics of the powder is also effective as a method to correct imperfections in skin color.
The blurring effect based on the diffuse reflection of spherical powder can correct skin surface unevenness such as prominence of pores and fine wrinkles. Thus, it is satisfactory from the standpoint of uniformly made-up skin. However, the blurring effect does not sufficiently correct imperfections in skin color.
A composite powder, in which the surface of flaky powder is uniformly covered with fine spherical resin powder, produces a strong gloss since the fine resin powder of less than 0.5 μm with precise arrangement in adhesion functions as a plane and causes normal surface reflection. In addition, since the refractive index of the resin powder is less than 1.5, the resin powder will mix with oil components in cosmetics and become transparent. Thus, expected diffuse reflection is not realized, and skin surface unevenness will become more conspicuous. Therefore, it is not satisfactory from the standpoint of uniformly made-up skin.
On the other hand, it is possible to hide imperfections in skin color by using a titanium oxide pigment with a high refractive index (2.69). However, its tone is matte without gloss, and the finished makeup foundation is pale because of strong light scattering due to the high refractive index. Thus, a natural finish can never be achieved. In addition, the hiding power is too strong to give clearness, and it produces only an unnatural impression compared with the actual skin.
In order to solve this problem, a powder containing titanium oxide doped with iron oxide was developed; thus, the make-up adapted to natural skin color was targeted by coloring with yellow orange pigment (Japanese Unexamined Patent Publication No. H07-3181). Although this powder made a certain contribution to a natural finish, the problem was not satisfactorily solved.
The composite powder, in which a substrate powder is covered with barium sulfate particles, was also developed (Japanese Examined Patent Publication No. H02-42388, Japanese Examined Patent Publication No. H02-42387, and Patent Publication No. 3184608). However, the diffuse reflection was low, and the correction of skin surface unevenness was poor; thus, the problem was not satisfactorily solved.
In addition, the powder development based on the structure of the skin tissue has been conducted to achieve the make-up finish close to the actual skin. However, there is a limit in imitating the complicated skin tissue, thus, not only a natural finish could not be achieved, but also the hiding power turned out to be low. Therefore, imperfections in skin color such as dullness and color irregularity could not be corrected, thus, satisfactory effects cannot be expected at the present stage.
In order to correct skin surface unevenness and imperfections in skin color, natural corrections based on the diffuse reflection and spectral characteristics of powder are most effective. Actually, the correction by combining substrate particles such as interference titanated mica and composite particles with good diffuse reflection is considered effective for makeup cosmetics. Since titanated mica has a strong surface reflection, the made-up skin has a glare. Thus, skin surface unevenness due to pores and fine wrinkles are conspicuous, and it is very difficult to achieve a natural beautiful finish.